Despite more than a century of research since the discovery of Mycobacterium tuberculosis, the aetiological agent of tuberculosis, by Robert Koch, this disease remains one of the major causes of human morbidity and mortality. There are an estimated 3 million deaths annually attributable to tuberculosis (Snider 1989), and although the majority of these are in developing countries, the disease is assuming renewed importance in the West due to the increasing number of homeless people and the impact of the AIDS epidemic (Chaisson et al., 1987; Snider and Roper, 1992).
Isonicotinic acid hydrazide or isoniazid (INH) has been used in the treatment of tuberculosis for the last forty years due to its exquisite potency against the members of the "tuberculosis" groups--Mycobacterium tuberculosis, M. bovis and M. africanum (Middlebrook, 1952; Youatt, 1969). Neither the precise target of the drug, nor its mode of action are known and INH treatment results in the perturbation of several metabolic pathways. There is substantial evidence indicating that INH may act as an anti-metabolite of NAD and pyridoxal phosphate (Bekierkunst and Bricker, 1967; Sriprakash and Ramakrishnan, 1970; Winder and Collins, 1968, 1969, 1970), and other data indicating that the drug blocks the synthesis of the mycolic acids, which are responsible for the acid-fast character of mycobacterial cell walls (Winder and Collins 1970; Quemard et al., 1991). Shortly after its introduction, INH-resistant isolates of Mycobacterium tuberculosis emerged and, on characterization, were often found to have lost catalase-peroxidase activity and to show reduced virulence in guinea pigs (Middlebrook et al., 1954; Kubica et al., 1968; Sriprakash and Ramakrishnan, 1970).
Very recently, INH-resistance has acquired new significance owing to a tuberculosis epidemic in the USA due to multi-drug resistant (MDR) variants of M. tuberculosis (CDC, 1990; 1991a, b) and the demonstration that such strains were responsible for extensive nosocomial infections of HIV-infected individuals and health care workers (Snider and Roper, 1992). In view of the gravity of this problem, there exists a need in the art to determine the relationship between INH-resistance and catalase-peroxidase production.
More particularly, there is a need in the art to understand the molecular mechanisms involved in drug sensitivity. In addition, there is a need in the art to develop a simple test permitting the rapid identification of INH-resistant strains. Further, there is a need in the art for reagents to carry out such a test.